Leonid MAC, NASA's first Astrobiology mission, is a series of 5 missions that took flight in aircraft during the years 1998, 1999, 2000, 2001, and 2002. By observing and studying meteor showers, the mission looked to learn how extraterrestrial materials may have been brought to Earth at the time of the origin of life. In addition, the interaction of meteoroids with the atmosphere generates molecules that may have played a role in the origin of life on Earth.

Using a varied mix of spectrometers, cameras, imagers, photometers and spectrographs each year, the Leonid MAC team flew in two separate aircraft to view and study the Leonid meteor storm.

Every year in mid-November, Earth passes close to an area of the debris trails left from the passing of periodic comet Tempel-Tuttle. The trail is littered with very small sand grain sized pebbles and dust that have eroded off the comet by solar wind and radiation. As Earth collides with this trail of dust each year, we usually can observe a meteor shower with up to 30 visible meteors per hour under clear dark skies. As pieces of this cometary debris enter Earth's atmosphere at an extremely high rate of speed, some 71 km per second, they cause the atmosphere to glow along their path leaving a visible ionized meteor trail. As Leonid meteors appear to emanate from, or point back to, the constellation Leo, it is known as the annual Leonid meteor shower.

Throughout the five years that this mission took flight many discoveries were made and the team was able to obtain many incredible images of the Leonid storms. Some of the discoveries made by the Leonid MAC team included the ability to weigh meteors by measuring the amount of iron atoms that are ablated in the wake of a meteor. The team also made the first detection of mid-infrared emissions coming from relatively faint meteors and the first mid-infrared spectroscopy of persistent meteor trains. Leonid MAC also detected, and later confirmed, the existence of a halo and shadow surrounding the head of bright Leonid meteors. Besides these discoveries and more, the team made near-real time reports to satellite operators during the 1999 and 2002 Leonid MAC missions.

2001's Leonid meteor storm was the most spectacular of the five missions.